1. Field of the Invention
This invention relates to a process for producing ligand developers of the following formula: ##STR2## where, each R.sup.1 can be the same or different substituent chosen from those that will not impair the functionality of the compound as a silver halide developing agent but preferably, each R.sup.1 is hydrogen.
2. Description of the Prior Art
Compounds of Formula 1 are known and have been described in at least the following U.S. Patents: U.S. Pat. Nos. 3,629,336; 3,772,368, 3,789,062; 3,812,191 and 3,903,169.
U.S. Pat. Nos. 3,772,368; 3,813,192 and 3,903,169 are particularly directed to methods for producing compounds of Formula 1. For example, U.S. Pat. No. 3,772,368 relates to a method involving reacting a Schiff base anion with a lactone to provide compounds of Formula 1 while U.S. Pat. No. 3,903,169 discloses a method for producing compounds of Formula 1 by way of a condensation reaction between a cyclopentanone anion and a lactone.
The method disclosed in U.S. Pat. No. 3,812,191 is somewhat different from the methods of the patents discussed above involving as it does, the preparation of a compound of the following formula: ##STR3## where, R.sup.1 is as defined before and each R provides a protecting function and is a substituent which can be removed by hydrolysis to provide the compound of Formula 1. Specifically, the method of U.S. Pat. No. 3,812,191 involves the preparation of a "protected" compound of Formula 2 e.g., the compound [3-(2,5-decathyloxyphenyl) propionyl] -2-cyclopentanone and the removal of the protecting groups -- the cathyloxy groups--to provide a compound of Formula 1.
According to the method disclosed in referenced U.S. Pat. No. 3,812,191, the cathyloxy groups of the [3-(2,5-dicathyloxyphenyl) propionyl] -2-cyclopentanone are removed by saponifying the protected compound in a substantially non-aqueous, solubilizing medium comprising a solution of an alkali metal hydroxide in an alcohol and acidifying the saponified product to a pH of between about 6.0 to about 7.0 and preferably between about 6.5 to about 7.0. The controlled acidification of the saponified product is an important factor in the method of U.S. Pat. No. 3,812,191 leading to commercially acceptable yields of compounds of Formula 1. For example, if the saponified product is acidified to a pH below 6.0 and particularly to a pH below 3.0, the predominant product is not the compound of Formula 1 but rather a cyclized compound of the following formula: ##STR4##
In accordance with the practice of the present invention it has been found that the cyclized compounds of Formula 3 are valuable intermediates in the production of developer ligands of Formula 1 since the cyclized compounds can be easily opened up by hydration to provide the compound of Formula 1.